Sending Mails with SMTP

Overview of SMTP in Go#

The package net/smtp implements the Simple Mail Transfer Protocol for sending mail. It contains a Client type that represents a client connection to an SMTP server:

Dial returns a new Client connected to an SMTP server.
Set Mail (=from) and Rcpt(= to)
Data returns a writer that can be used to write the data, here with buf.WriteTo(wc).

package main
import (
"bytes"
"log"
"net/smtp"
)
func main() {
    // Connect to the remote SMTP server.
    client, err := smtp.Dial("smtp.gmail.com:587")
    if err != nil {
        log.Fatal(err)
    }
    // Set the sender and recipient.
    client.Mail("sender email address")
    client.Rcpt("receiver email address")
    // Send the email body.
    wc, err := client.Data()
    if err != nil {
        log.Fatal(err)
    }
    defer wc.Close()
    buf := bytes.NewBufferString("This is the email body.")
    if _, err = buf.WriteTo(wc); err != nil {
        log.Fatal(err)
    }
}

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SMTP Server

In the code above, we need the package net/smtp, which is imported at line 5. First, we need to connect to an active remote SMTP server, which is done with the Dial method at line 10, creating a client instance. Error-handling (from line 11 to line 13) exits the program on error.

We set up the sender and receiver email address at line 15 and line 16, respectively. Line 18 constructs the Data method on client, which makes a client writer wc with similar error-handling from line 19 to line 21. At line 22, we make sure that the writer wc will be closed. Then, at line 23, we make a buffered string and write it to wc at line 24. This if-statement is combined with error-handling, logging an eventual error and exiting the program at line 25.

The function SendMail can be used if authentication is needed and when you have a number of recipients. It connects to the server at addr, switches to TLS (Transport Layer Security encryption and authentication protocol), authenticates with the mechanism if possible, and then sends an email from address from to addresses to, with the message msg:

func SendMail(addr string, a Auth, from string, to []string, msg []byte) error

Go through the following illustrations that explain how to set a Gmail account for sending an email before running a program.

This code requires the following environment variables to execute:

GOROOT

/usr/local/go

GOPATH

//root/usr/local/go/src

PATH

//root/usr/local/go/src/bin:/usr/local/go/bin://root/usr/local/go/src/bin:/usr/local/go/bin://root/usr/local/go/src/bin:/usr/local/go/bin://root/usr/local/go/src/bin:/usr/local/go/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

/

main.go

package main
import (
    "fmt"
    "net/smtp"
)
// smtpServer data to smtp server
type smtpServer struct {
 host string
 port string
}
// serverName URI to smtp server
func (s *smtpServer) serverName() string {
 return s.host + ":" + s.port
}
func main() {
    // Sender data.
    from := "sender email address"
    password := "password" // you can enter original password or password generated with App password
    // Receiver email address.
    to := []string{
        "first receiver email address",
        //"second receiver email address",
    }
    // smtp server configuration.
    smtpServer := smtpServer{host: "smtp.gmail.com", port: "587"}
    // Message.
    message := []byte("Enter the message you want to send.")
    // Authentication.
    auth := smtp.PlainAuth("", from, password, smtpServer.host)
    // Sending email.
    err := smtp.SendMail("smtp.gmail.com:587", auth, from, to, message)

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Overview of SMTP in Go#

Explanation#

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